I disagree with if it sounds like its gonna come apart, it will. We used GMC 6 cylinders in the 50's and 60's to haul gasoline. We constantly kept them above 3k. My first semi was a 550 GMC with a 370 V8. I down shifted at 3800 and up shifted at 42 to 4400. Solid tappets and steel fans make a lot of noise, but that's just how they were. Back in those days, the people who had engine trouble were the ones who lugged their engines. Rod bearings need high rpms to oil properly and piston skirts wear in a hurry when engines are lugged. I don't try to fix or calibrate old speedos. A gps works good enough for me.
